Codes Not Generated For CD Version

We are using the PayPal web api you provide to accept PayPal order and then email the customer with the activation code and other information.

We have customers complain that they do not get the email when they order our software in CD form, it works fine when they order the download.

In the Payment.php file, the section below will result in the confirmation email being sent successfully & I see a code being generated when I look at my LimeLm dashboard for the product..., if I change the line:

<input type="hidden" name="no_shipping" value="1"/>

to:

<input type="hidden" name="shipping" value="3.95"/>

not only does the code not get generated but the email is not sent. Any ideas why this is happening please?

if ($UsePayPal) { ?> <input type="hidden" name="cmd" value="_xclick"/> <input type="hidden" name="business" value="<?=$PayPalEmail?>"/> <input type="hidden" name="undefined_quantity" value="1"/> <input type="hidden" name="item_name" value="<?=$AppName?> license"/> <input type="hidden" name="item_number" value="COM2015-CD"/> <input type="hidden" name="no_shipping" value="1"/> <input type="hidden" name="no_note" value="1"/> <input type="hidden" name="currency_code" value="<?=$Currency?>"/> <input type="hidden" name="lc" value="US"/> <input type="hidden" name="rm" value="2"/> <input type="hidden" name="return" value="<?=$ThankYouPage?>"/> <input type="hidden" name="cancel_return" value="<?=$BuyPage?>"/> <input type="hidden" name="notify_url" value="<?=$CheckScript.'?paypal=1'?>"/><?php if ($YourLogo) echo '<input type="hidden" name="image_url" value="'.$YourLogo.'"/>';}